Fresnel zone

About: Fresnel zone is a research topic. Over the lifetime, 2337 publications have been published within this topic receiving 37650 citations.

High-frequency filtered images of an optically thick edge

Abstract: Peculiarities of high-frequency filtering (contouring) of images of symmetric thick (extended along the optical axis) edge are investigated in analytical form by the Kirchhoff–Fresnel approximation. They are based on a model of equivalent diaphragms (transparencies) earlier proposed by the authors [J. Opt. Soc. Am.71, 483 (1981)]. Expressions for the fields in special cases of perfect absorption and reflection are derived. For the case of slight volumetric effects, a structure of the contoured images of the front and back faces is shown to be similar to a structure of the contoured image of the plane edge. But the influence of the extension causes a shift of the basic minimum position proportional to the size of the Fresnel zone. When volumetric effects are significant, the profile of the filtered image of the front face has a single maximum (instead of a double one). Here the structure of the filtered image of the back face depends to a great extent on the reflection properties of the inner surface, changing from the form with a double maximum to the form with a single one. There is agreement between theoretical and experimental results.

Optical trapping methods and apparatus employing one or more fresnel zone plates

Abstract: Methods and apparatus (1100) for trapping fluid-borne object (s) (212) using one or more Fresnel zone plates (202) located in proximity to a fluid medium (208). Optical tweezers based on one or more Fresnel zone plates may be integrated with a microfluidic structure (e.g., chambers, channels) (1104) of various geometries so as to form one or more optical traps (215) within a fluid medium contained by the microfluidic structure (s). Three-dimensional trapping of objects can be obtained with stiffness comparable to that of conventional optical tweezers based on a microscope objective. In one example, a single Fresnel zone plate is particularly configured to form multiple optical traps upon irradiation, so as to trap multiple objects simultaneously. Exemplary applications of the methods and apparatus disclosed herein include determination of various fluid medium properties (e.g., velocity, refractive index, viscosity, temperature, pH) and object sorting.

G.T.D. analysis of the near-field patterns of pyramidal horns

Abstract: A technique of analysing the principal-plane near-field patterns of pyramidal horns excited in the dominant mode based on the uniform geometrical theory of diffraction (u.g.t.d.)1, 2 is presented in this paper. The geometrical-optics field is derived by approximating the horn as a quasipyramidal horn waveguide.9 Numerical computations of the near-field amplitude patterns of a typical pyramidal horn based on the g.t.d. technique detailed here well correlate with the measured patterns, justifying the validity of the analysis presented. Further, the analysis presented is valid for any arbitrary field point (located in the principal planes) so that pattern computation is possible in the near field or in the Fresnel zone or in the far field.

Theoretical Considerations on Acoustic Field Formed by Fresnel-Zone-Type Focusing Radiator : Ultrasonic Propagation and Field

Abstract: Focusing performance of Fresnel-zone-type ultrasonic focusing systems is evaluated by calculating field distributions for an equivalent radiator composed of concentric annular-transducer elements, and is compared with that of a concave radiator. It is demonstrated that the Fresnel-zone-type radiator presents almost the same focused field as the corresponding concave one and gives reduced sidelobes uner the existence of propagation loss. Focusing characteristics of radiators with inactivated transducer elements in the central part are also examined.

Fault imaging in sparsely sampled 3D seismic data using common-reflection-surface processing and attribute analysis – a study in the Upper Rhine Graben

Abstract: Cost reduction in seismic reconnaissance is an issue in geothermal exploration and can principally be achieved by sparse acquisition To address the adherent decrease in signal/noise ratio, the common‐reflection‐surface method has been proposed We reduced the data density of an existing 3D dataset and evaluated the results of common‐reflection‐surface processing using seismic attributes The application of the common‐reflection‐surface method leads in all cases to an improvement of the signal/noise ratio The most distinct improvement can be seen in the low fold regions The improvement depends strongly on the midpoint aperture, and there is a tradeoff between reflector continuity and horizontal resolution If small scale targets are to be imaged, a small aperture size is necessary, which may be far below the Fresnel zone for a specific reflector The substantial reduction of the data density leads in our case to an irrecoverable information loss